The invention discloses a single-cylinder opposed double-piston type free piston linear generator. The linear generator comprises a generator, two sets of two-stroke engines, an auxiliary motor I andan auxiliary motor II, the auxiliary motor I and the auxiliary motor II are symmetrically arranged on the two axial sides of the generator. The auxiliary motor I and the auxiliary motor II are connected with the generator; the auxiliary motor I and the auxiliary motor II are connected with the two-stroke engines; each two-stroke engine comprises an air cylinder body, a cylinder cover, a spark plug, an oil sprayer, a piston, a crankcase kit and a connecting rod. The auxiliary motor I, the auxiliary motor II and the generator are coaxially arranged, the generator is connected with the auxiliarymotor I and the auxiliary motor II, and preset axial distances are arranged between a generator stator and two windings closest to an auxiliary motor I stator and between a generator stator and two windings closest to the auxiliary motor II stator respectively. The invention solves the problem of long response time of motor working mode switching, ensures that the piston smoothly reaches a specified position, and enables the free piston linear generator to stably operate.